Multi coriolis structured gyroscope

ABSTRACT

A resonator paradigm, where the resonator structure is made up of a very large number of small, coupled Coriolis sensitive units arranged in a periodic 1D or 2D (and, possibly, in the future, 3D) structure to create a Coriolis-sensitive “fabric” that supports a large number of Coriolis-coupled “supermodes. Such a “fabric” can be shaped into arbitrary “waveguides” that propagate either pulses of excitation that are Coriolis-coupled, thus enabling an acoustic version of a FOG-type gyroscope (where a pulse of excitation travels along a passive waveguide and it&#39;s phase/time delay is measured), or support multiple “stationary” Coriolis-coupled vibration modes analogous to optical laser modes in an RLG where counter-propagating modes of oscillation are maintained at constant amplitude via a continuous addition of energy.

PRIORITY CLAIM

The present application is a continuation of, and claims prioritybenefit to, co-pending and commonly assigned U.S. non-provisional patentapplication entitled, “Multi Coriolis Structured Gyroscope,” applicationSer. No. 15/337,627, filed Oct. 28, 2016, which claims priority toprovisional application entitled, “Multi Coriolis Structured Gyroscope,Application Ser. No. 62/248,983, filed Oct. 30, 2015. The aboveapplications are hereby incorporated by reference into the currentapplication in their entirety.

BACKGROUND 1. Field

The present disclosure relates generally to resonating structures. Moreparticularly, the present disclosure relates to Coriolis coupledgyroscope devices.

2. Related Art

Current State-of-the-art micro-electro-mechanical sensors (MEMS)gyroscope technology utilizes either well-defined mass-on the springtype resonators (Foucault pendulum, tuning fork gryoscope (TFG),quad-mass gyroscope (QMG)), or structures supporting a pair of Corioliscoupled modes where the mass and the spring are distributed throughoutthe resonator structure (hemispherical resonating gyroscope (HRG),annular ring, disc resonating gyroscope (DRG)). These devices sufferfrom limitations in limited utilization of the available devicefootprint, low signal to noise ratio and fabrication imperfectionscausing noise.

SUMMARY

The following summary is included in order to provide a basicunderstanding of some aspects and features of the invention. Thissummary is not an extensive overview of the invention and as such it isnot intended to particularly identify key or critical elements of theinvention or to delineate the scope of the invention. Its sole purposeis to present some concepts of the invention in a simplified form as aprelude to the more detailed description that is presented below.

Embodiments of the invention are directed to a resonator structure thatis made up of a very large number of small, coupled Coriolis sensitiveunits arranged in a periodic one dimensional (1D) or two dimensional(2D) (and, possibly, in the future, three dimensional (3D)) structure,thus creating a Coriolis-sensitive fabric that supports a large numberof Coriolis-coupled supermodes. Such a fabric can be shaped intoarbitrary waveguides that propagate pulses of excitation (signals) thatare Coriolis-coupled, thus enabling an acoustic version of a fiber opticgyroscope (FOG)-type gyroscope (where a pulse of excitation travelsalong a passive waveguide and its phase delay and/or time delay delay ismeasured).

Embodiments of the invention also relate to a resonator structure thatsupports multiple stationary Coriolis-coupled vibration modes analogousto optical laser modes in a ring laser gyroscope (RLG) wherecounter-propagating modes of oscillation are maintained at constantamplitude via a continuous addition of energy.

According to one aspect of the invention, a gyroscope is disclosed thatincludes a resonator comprising a Coriolis-sensitive fabric, theCoriolis-sensitive fabric comprising a plurality of coupledCoriolis-sensitive units arranged in a periodic structure.

According to another aspect of the invention, a gyroscope is disclosedthat includes a resonator body comprising a Coriolis-sensitive fabric,the Coriolis-sensitive fabric comprising a plurality of coupledCoriolis-sensitive units arranged in a periodic structure, wherein theplurality of coupled Coriolis-sensitive units are shaped into waveguidesand support a large number of Coriolis-coupled supermodes.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and constitute apart of this specification, illustrate one or more examples ofembodiments and, together with the description of example embodiments,serve to explain the principles and implementations of the embodiments.

FIG. 1A is a schematic view of a periodic 1-dimensionalCoriolis-sensitive structure in accordance with one embodiment of theinvention.

FIG. 1B is a schematic view of a periodic 1-dimensionalCoriolis-sensitive structure in accordance with one embodiment of theinvention.

FIG. 1C is a schematic view of a periodic 1-dimensionalCoriolis-sensitive structure in accordance with one embodiment of theinvention.

FIG. 1D is a schematic view of a periodic 1-dimensionalCoriolis-sensitive structure in accordance with one embodiment of theinvention.

FIG. 1E is a schematic view of a periodic 2-dimensionalCoriolis-sensitive structure in accordance with one embodiment of theinvention.

FIG. 1F is a schematic view of a periodic 2-dimensionalCoriolis-sensitive structure in accordance with one embodiment of theinvention.

FIG. 2A is a schematic diagram of a sensor die ballistic pulse(FOG-type) in accordance with one embodiment of the invention.

FIG. 2B is a schematic diagram of a counter-propagating mode (RLG-type)in accordance with one embodiment of the invention.

FIG. 3 is a flow diagram of control electronics for the gyroscope sensorin accordance with one embodiment of the invention.

DETAILED DESCRIPTION

In the following description of embodiments of the invention, referenceis made to the accompanying drawings which form a part hereof, and inwhich is shown by way of illustration a specific embodiment in which theinvention may be practiced. It is to be understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from the scope of the present invention.

Overview

MEMS gyroscopes use the coriolis effect to measure the angular rate ofmovement (the rotational movement) of the gyroscope. Gyroscopestypically determine the rotational movement using an internally movingproof mass. A typical electromechanical gyroscope comprises a suspendedproof mass, gyroscope case, pickoffs, torquers and readout electronics.The proof mass—a resonator—is suspended from a base plate that attachedto the resonator at a stiff central attachment area. The proof massvibrates when the gyroscope is moved; sensors in the gyroscope canmeasure the vibration of the separate masses, and the angular rate ofmovement can be extracted from the measured data.

Embodiments of the invention relate to resonators where the resonatorstructure is made up of a very large number of small, coupled Coriolissensitive units arranged in a periodic 1D or 2D (and, possibly, in thefuture, 3D) structure, thus creating a Coriolis-sensitive fabric thatsupports a large number of Coriolis-coupled supermodes. Exemplarystructures of this type are shown in FIGS. 1A-1F and will be describedin further detail hereinafter.

Such a fabric can be shaped into arbitrary waveguides that propagateeither pulses of excitation that are Coriolis-coupled, thus enabling anacoustic version of a FOG-type gyroscope (where a pulse of excitationtravels along a passive waveguide and its phase delay and/or time delayis measured), or support multiple stationary Coriolis-coupled vibrationmodes analogous to optical laser modes in an RLG (wherecounter-propagating modes of oscillation are maintained at constantamplitude via a continuous addition of energy).

Existing electrostatic excitation, tuning, and sensing technology enablean acoustic equivalent of such devices as a positive gain section (akinto a laser gain medium) via the use of parametric excitation,waveguides, beam splitters, directional couplers, distributed feedbackstructures, diffraction gratings, etc. Techniques such as mode locking,both active and passive, can be utilized to precisely control theexcitation patterns. In addition, electrostatic spring softening can beutilized to control the effective refractive index of the fabric in botha static and a dynamic manner, thus enabling precise control andmanipulation of the excitation pattern.

In embodiments of the present invention, shaping the array of sensorunits into arbitrary waveguides that propagate pulses of excitation thatare Coriolis-coupled has a variety of advantages over conventionalgyroscopes. For example, the benefits of utilizing embodiments of thepresent invention are:

-   -   1. efficient utilization of the available device footprint;    -   2. the ability to support large vibration amplitudes thus        increasing the Coriolis force and the sensor signal to noise        ratio (SNR);    -   3. the ability to apply advanced excitation control and signal        processing techniques developed in the optical realm;    -   4. the tendency to average out local fabrication imperfections        by utilizing large ensembles of Coriolis-sensitive units; and    -   5. the ability to have multiple virtual gyroscopes operating on        the same physical fabric but separated in frequency, thus        creating a possibility of utilizing the bias correlations from        different gyroscoping modes to detect and cancel out bias drift        while obviating the need for a large number of separate hardware        signal channels.

Embodiments of the invention are a first step in the direction ofevolving Coriolis sensitive resonator structures into smart activematerials with Coriolis-sensing properties. Advantages of such smartactive materials include efficient sensor miniaturization, environmentalrobustness, high shock survivability, and ease of integration intocomplex navigation systems.

Conventional MEMS gyroscopes utilize the Coriolis force to measurerotation, which for a moving point mass is given by the well-knownequation:

F _(c)=3m{right arrow over (v)}×{right arrow over (Ω)}

For a vibratory type sensor, where the motion is periodic, the velocityis proportional to the product of amplitude and frequency:

v∝αω

Thus, the relevant figure of merit for a Coriolis-sensing structurebecomes:

mαω

To increase the Coriolis signal (and thus the performance of thesensor), either the moving mass, the frequency, or the motion amplitudeare increase. Other design considerations affect the choice of thevibration frequency, such as electronics noise spectrum, vibration andshock considerations, and materials properties. For instance, to berobust to a 20000 g shock, the structure has to have a translationalresonance frequency above 3050 kHz, depending on the available structureclearance. These and other considerations suggest that frequenciesbetween 100 and 500 kHz will probably be in the optimal design range.Conventional homogeneous materials support Coriolis-coupled bulk modepairs (for example, the transverse acoustic branches areCoriolis-coupled), but due to the limitations of achievable strain inthe bulk, the product αω remains nearly constant and small over thewhole range of utilizable frequencies (up to 100s of MHz). At higherfrequencies other loss mechanisms (such as Akhiezer damping) quicklybegin to dominate greatly increasing the damping and thus the intrinsicnoise of the system. In addition, because of the high elastic modulus ofcommon materials (in the 100 GPa range), the wavelengths at lowerfrequencies are quite long, thus precluding the use of compactstructures. With the realistic material densities ranging over not morethan on order of magnitude (2.5 gm/cm³ for Si on the light side up to22.6 gm/cm³ for Iridium, the densest material presently known), theprospect for increasing the figure of merit by increasing the massfactor m in the mαω is limited. Accordingly, what is needed is astructure that greatly decreases the material stiffness thus loweringthe effective wavelength and proportionately increasing the availablemotion amplitude, while maintaining a material density similar to thebulk, to achieve the multiple orders of magnitude increase in signalrequired to meet advanced navigation system requirements.

To achieve the required decrease in the material stiffness, embodimentsof the invention are directed to an engineered material consisting of aperiodic array of unit cells that maintains the density fairly close tothe bulk (above 50%) while reducing the effective (long range, overmultiple unit cells) stiffness by many orders of magnitude. In thismanner, the effective elastic modulus for lower frequency modes (wherethe wavelength is much greater than the unit cell spacing) can be tunedto almost arbitrarily low values thus lowering the effective acousticpropagation velocity:

$c = \sqrt{\frac{K}{\rho}}$

where K is the effective modulus, and ρ is the density.

The resulting wavelengths in the optimal range can thus be made fairlyshort, enabling the use of compact structures and proportionallyincreasing the Coriolis interaction time of the vibration patterntraveling over a fixed distance (such as in multiple loops of avibration guiding structure, an acoustic analogue to a FOG gyroscope).

Coriolis-Sensitive Unit Cell

A Coriolis-sensitive atom of the fabric of embodiments of the inventionis essentially a very simple mass-on-the spring. The challenge is todesign the geometry in such a way as to most efficiently utilize theavailable physical sensor area. For the nominal size profile of 1 cm³this translates into roughly a 5×5 mm available silicon footprint(allowing room for vacuum packaging, mechanical support and electronicsintegration). Given a fabrication process profile (primarily, theachievable DRIE trench aspect ratio), and recognizing that the moreunits are packed into the active structure, the more the systemapproaches the desired Coriolis-sensitive “continuum” behavior, anoptimal unit size can be determined. Since the trench is essentiallywasted space (albeit necessary to provide the needed fabric function),the optimal cell size lies at about 50-70% of solid areal fill factor.Thus, the cell size is about 3×-4× the minimum trench width for thesimplest cell designs.

An exemplary cell design is shown in FIG. 1A. In FIG. 1A, the celldesign 100 is a periodic one-dimensional structure. The cell design 100includes a plurality of cell components 104 that repeat. Each cellcomponent 104 includes a square section 106 and a connector element 108.The connector element 108 includes a horizontal bar 112, a vertical bar114 and another horizontal bar 116.

Another exemplary cell design is shown in FIG. 1B. In FIG. 1B, the celldesign 120 is also a periodic one-dimensional structure that is acorrugated ribbon type. The cell design 120 also includes plurality ofcell components 124 that repeat. Each cell component 124 includes ahorizontal bar 128, a first vertical bar 130, another horizontal bar132, and a second vertical bar 134.

A slightly more complex cell design with a bias electrode enabling thecontrol of the excitation frequency (and thus propagation parameters) isshown in FIG. 1C. The design shown in FIG. 1C requires a size increaseof another 2× trench widths. The cell design 140 includes a plurality ofcell components 144 that repeat. Each cell component 144 includes asquare section 146 and a connector element 148. The connector element148 includes a horizontal bar 152, a vertical bar 154 and anotherhorizontal bar 156. Each cell component 144 further includes anelectrode element 158.

FIG. 1D shows an alternate complex cell design with a bias electrode.The cell design 160 also includes plurality of cell components 164 thatrepeat. Each cell component 164 includes a horizontal bar 168, a firstvertical bar 170, another horizontal bar 172, and a second vertical bar174. Each cell component 164 further includes first and second electrodeelements 176, 178.

FIG. 1E shows a two-dimensional example of a periodic structureaccording to one embodiment of the invention. The structure includes aplurality of cell components 180 that repeat. Each cell component 180includes a square section 184 and connector elements 188.

FIG. 1F shows an alternative two-dimensional example of a periodicstructure. The structure includes a plurality of cell components 190that repeat. Each cell component 190 includes a triangle section 194 andconnector elements 198.

For a number of widely available DRIE processing tools, the trench widthcan be reliably set at 1 μm, thus allowing a cell size in the 3-6 μmrange. For a nominal die footprint, the die will have an array of about1,000×1,000 unit cells, enabling a fairly large number of supermodesthat have over 30-50 units cells/wavelength thus operating in aquasi-continuum regime. It will be appreciated that the number of unitcells in the array may be less than 1,000 or more than 1,000.

Sensor Designs

FIG. 2A shows an exemplary ballistic type gyroscope sensor. The sensor200 includes a resonator body 204 that includes a one-dimensional,Coriolis-sensitive waveguide fabric 206 formed of a first waveguide 208a and a second waveguide 208 b, each of which may be formed of aperiodic structure depicted in FIGS. 1A-1D and arranged as a continuousstring. The sensor 200 further includes a travel path formed by thefirst waveguide 208 a and the second waveguide 208 b form twocounter-propagating loops traveling between a signal generation unit222, which outputs signals (excitation pulses), and two measurementlocations 216, 220, respectively, from which a phase and/or a time delaymay be determined by control electronics.

The one-dimensional, Coriolis-sensitive fabric 206 is utilized (in thisexample illustrated in FIG. 2A as a corrugated ribbon type) to propagatea signal (an excitation pulse) from the signal generation unit 222located at the excitation pulse launch point 212 over a large number ofturns in the first waveguide 208 a and the second waveguide 208 b to themeasurement locations 216, 220. This increases the sensor baseline toeffectively about a 1 meter long in a chip of about a 5 mm×5 mmfootprint. The first waveguide 208 a and the second waveguide 208 b,which are counter-propagating loops, are utilized to provideanti-correlated phase and/or time delayed signals that are measured atthe two measurement locations 216, 220, thus cancelling the correlated(common mode) bias drift.

FIG. 2B shows an alternative exemplary gyroscope sensor. The sensor 250includes a resonator body 252 having an active two-dimensional (2D),Coriolis-sensitive waveguide fabric 254, which may be formed of theperiodic structure depicted in FIGS. 1E-1F. The active 2D waveguidefabric 254 supports multiple counter-propagating Coriolis-sensitivemodes in the manner of an RLG. The waveguide fabric 254 of sensor 250further includes a guiding higher index area 256, which may be an areaof lower stiffness than the remainder of the waveguide fabric 254. Thewaveguide fabric 254 of sensor 250 also includes counter-propagatingfirst and second mode loops 258 a, 258 b (forming a first travel path260 a and a second travel path 260 b, respectively, along which signalstravel), first and second amplifying gain regions 262 a, 262 b and firstand second vibration pick-offs 266 a, 266 b. Counter-propagating modesof oscillation are maintained at constant amplitude via a continuousaddition of energy provided by the first and second amplifying gainregions 262 a, 262 b.

The waveguide fabric 254 is physically attached to other portions of theresonator body 252 in a manner that isolates the active waveguide fabric254 portion from the outside (external) vibration and stress. Thewaveguide fabric 254 structure can be active (utilizing tuningelectrodes to localize the excitation travel path) and/or passive(utilizing a stiffness grading to accomplish the same).

A section of the waveguide fabric 254 contains a plurality of tuningelectrodes and first and second amplifying gain regions 262 a, 262 bused for parametric excitation, thus providing signal gain and enablingoscillation to persist in the waveguide fabric 254 and thecounter-propagating first and second mode loops 258 a, 258 b.Strategically placed pick-off points 266 a, 266 b are used to sample theexcitation and measure the relative phase and/or time delay of thecounter-propagating mode pairs, thus providing multiple collocatedvirtual gyroscopes.

Electrostatic spring softening can be utilized to control the effectiverefractive index of the waveguide fabric 254 in both a static and adynamic manner, thus enabling precise control and manipulation of theexcitation pattern.

It is generally known that a large array of correlated gyroscopes arecapable of performance far exceeding the performance of a single sensor.The fact that the same structure is used to achieve multiple gyroscopeoutputs is believed to result in a high degree of correlation betweenthe signals and enables advanced signal processing that extracts andcompensates for bias drift.

Electronics

An exemplary control electronics scheme 300 is shown in FIG. 3. As shownin FIG. 3, the control electronics 300 includes digital signalprocessing (DSP) control loops 304, bias digital to analog converters(DACs) 308 and driving digital to analog converters (DACs) 312, a sensor316, a sensor front end 320 and sensor analog to digital converters(ADCs) 324. As shown in FIG. 3, the DSP sensor control loop 304 providesinput to bias DACs 308 and driving DACs 312, which are connected to thesensor 316. The sensor front end 320 communicates with the sensor ADCs324, which in turn provide feedback to the DSP sensor control loops 304.

Since the multiple modes are separated in frequency, a singledifferential pair of excitation, sensing, and tuning hardware can beemployed, with the multiple control loops implemented in the DigitalSignal Processing (DSP) realm. This greatly simplifies the electronicsand allows for efficient miniaturization. The architecture is alsoscalable, as additional modes (virtual gyros) can be added if necessaryvia simple changes in firmware with no ASIC hardware or physics packagemodifications.

The invention has been described in relation to particular examples,which are intended in all respects to be illustrative rather thanrestrictive. Those skilled in the art will appreciate that manydifferent combinations will be suitable for practicing the presentinvention. Moreover, other implementations of the invention will beapparent to those skilled in the art from consideration of thespecification and practice of the invention disclosed herein. Variousaspects and/or components of the described embodiments may be usedsingly or in any combination. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims.

What is claimed is:
 1. A gyroscope comprising: a resonator having asensor area and an array of coupled sensor units arranged in a periodicstructure forming a Coriolis-sensitive fabric configured to sense aCoriolis effect associated with movement of the gyroscope and a signalgeneration unit located at an excitation point within the sensor areaand configured to output a first signal and a second signal, the firstsignal traveling through a first portion of the sensor units along afirst travel path from the excitation point to a first measurementlocation within the sensor area and the second signal traveling througha second portion of the sensor units along a second travel path from theexcitation point to a second measurement location within the sensorarea; a first vibration pick-off point located at the first measurementlocation; a second vibration pick-off point located at the secondmeasurement location; and control electronics coupled with the firstvibration pick-off point and the second vibration pick-off point, thecontrol electronics configured to: receive the first signal from thefirst measurement location, receive the second signal from the secondmeasurement location, and determine a comparative signal characteristicbased on the received first signal and the second signal; wherein thefirst signal propagates along the first travel path in a first directioncounter to a second direction in which the second signal propagatesalong the second travel path; and wherein the periodic structurecomprises a two-dimensional structure.
 2. The gyroscope of claim 1,wherein the control electronics are further configured to determine arotation of the gyroscope based on the determined comparative signalcharacteristic.
 3. The gyroscope of claim 1, wherein the first signaland the second signal form counter-propagating mode pairs, and whereinthe comparative signal characteristic is a relative phase of thecounter-propagating mode pairs.
 4. The gyroscope of claim 1, wherein thecomparative signal characteristic is a phase delay between the firstsignal and the second signal at the first measurement location and thesecond measurement location, respectively.
 5. The gyroscope of claim 1,wherein the resonator comprises a resonator body, and wherein theresonator body constitutes a proof mass.
 6. The gyroscope of claim 1,wherein the fabric isolates the resonator from external stress andvibration.
 7. The gyroscope of claim 1, wherein the sensor area is 5millimeters by 5 millimeters, and wherein the array of coupled sensorunits is square and comprises 1,000 sensor units×1,000 sensor units. 8.The gyroscope of claim 1, wherein the comparative signal characteristicis a time delay between the first signal and the second signal at thefirst measurement location and the second measurement location,respectively.
 9. The gyroscope of claim 1, further comprising at leastone amplifying gain region including tuning electrodes configured toincrease an amplitude of the counter-propagating first signal and thesecond signal.
 10. The gyroscope of claim 1, wherein the first signaland the second signal are each pulses of excitation, and wherein thearray of coupled sensor units are electromechanically coupled.
 11. Agyroscope comprising: a resonator body having a sensor area and an arrayof coupled sensor units comprising a first plurality of sensor unitsarranged in a periodic structure forming a Coriolis-sensitive fabricconfigured to sense a Coriolis effect associated with movement of thegyroscope and a second plurality of sensor units located at anexcitation point within the sensor area and configured to output a firstsignal and a second signal, the first signal traveling through a firstportion of the first plurality of sensor units along a first travel pathfrom the excitation point to a first measurement location within thesensor area and the second signal traveling through a second portion ofthe first plurality of sensor units along a second travel path from theexcitation point to a second measurement location within the sensorarea; a first vibration pick-off point located at the first measurementlocation; a second vibration pick-off point located at the secondmeasurement location; and control electronics coupled with the firstvibration pick-off point and the second vibration pick-off point, thecontrol electronics configured to: receive the first signal from thefirst measurement location, receive the second signal from the secondmeasurement location, determine a comparative signal characteristicbetween the first signal and the second signal; and determine a rotationof the gyroscope based on the determined comparative signalcharacteristic; wherein the first signal propagates along the firsttravel path in a clockwise direction counter to a counter-clockwisedirection in which the second signal propagates along the second travelpath; and wherein the periodic structure comprises a two-dimensionalstructure.
 12. The gyroscope of claim 10, wherein the controlelectronics are further configured to determine a rotation of thegyroscope based on the determined comparative signal characteristic. 13.The gyroscope of claim 10, wherein the first signal and second signalform counter-propagating mode pairs, and wherein the comparative signalcharacteristic is a relative phase of the counter-propagating modepairs.
 14. The gyroscope of claim 1, wherein the comparative signalcharacteristic is a phase delay between the first signal and the secondsignal at the first measurement location and the second measurementlocation, respectively.
 15. The gyroscope of claim 10, furthercomprising at least one amplifying gain region including tuningelectrodes configured to increase an amplitude of the first signalbetween the excitation point and the first measurement location.
 16. Thegyroscope of claim 10, wherein the resonator comprises a resonator body,and wherein the resonator body constitutes a proof mass.
 17. Thegyroscope of claim 10, wherein the fabric isolates the resonator fromexternal stress and vibration.
 18. The gyroscope of claim 10, whereinthe sensor area is 5 millimeters by 5 millimeters, and wherein the arrayof coupled sensor units is square and comprises 1,000 sensor units×1,000sensor units.
 19. The gyroscope of claim 1, wherein the first signal andthe second signal are each pulses of excitation, and wherein the arrayof coupled sensor units are electromechanically coupled.